In a number of technical plants, for example power plants for power generation, compressors and compressor units are used to compress different gaseous and/or liquid fluids and deliver them for further use.
In the case of a gas turbine plant for example the air taken in is compressed by means of a compressor before it is fed into the combustion chamber.
To ensure reliable turbine operation, there is provision for temperature monitoring, of turbine blades for example, according to U.S. Pat. No. 5,306,088. Optical fibers are used for temperature acquisition.
For safe and non-destructive operation the quantity delivered must not drop below what is known as the critical delivery rate (also referred to as the pump limit or stability limit). Should the fluid flow to be processed instantaneously by a compressor be less than said critical delivery rate of the compressor, it is possible for the flow to cease suddenly during the compression process, on the compressor blades in particular, whereupon a mechanical overload is possible, as this causes much higher instantaneous pressures to occur than during normal operation. It can also result in the unwanted generation of low-frequency vibration and it is also possible for the compressor to overheat.
To achieve the highest possible level of efficiency of the compressor, its working point is frequently set as close as possible to its pump limit or its so-called maximum absorption capacity.
Values should however not be below or above the two limit values mentioned where possible during operation, in order to prevent damage to the plant.
A regulation system is therefore required for most compressors used in technical plants.
In the case of known regulation systems a model of the flow phenomena is used for example, with limit characteristics being determined for operation, which should not be infringed.
Depending on the quality of the model used for the flow phenomena and the accuracy of measurements taken during a commissioning phase, relative optimization of the working point can be effected and it can be moved closer to the limit characteristics.
However it is not possible in this process to dispense with a safety interval in relation to the limit characteristics, as known measuring methods, for temperature acquisition for example, can only be used in individual cases because of the high pressures and temperatures in the compressors. It is therefore very difficult to determine the pump limit of a compressor during the commissioning phase, without causing an unwanted high load level to occur.